- The most important insect pest of Minnesota-grown apples is the apple maggot (Rhagoletis pomonella).
- Appears in early July and is active until September. Peak activity occurs from late July through early August.
- Heavily infested fruit is distorted, inedible and suitable only for cider or animal feed.
- There are nonchemical and chemical options for managing apple maggots.
How to identify apple maggot
The adult fly is ¼ Inch long, smaller than a common housefly.
- It has characteristic dark markings on the clear wings and a conspicuous white spot where the thorax joins the abdomen.
- Has three (male) or four (female) white stripes on the abdomen.
Life cycle of apple maggot
Adult apple maggots begin to emerge from the soil starting about July 1, continuing through most of the summer.
- Adult flies often leave and feed outside the orchard, in wooded or brushy areas.
- They return to lay eggs just under the skin of apples.
- Each female fly can lay hundreds of eggs.
- Once eggs hatch, larvae feed for three to four weeks.
- When apples drop to the ground, the larvae transform into pupae in the soil.
- Pupae spend the winter underground, emerging as adults the following summer.
Damage caused by apple maggot
Apple maggot lays eggs in the fruit and the fruit becomes pitted and misshapen.
Each "sting” or hole created by the female fly as she lays an egg, forms a tiny spot or dimple.
Pulp breaks down, discolors and starts to rot as a result of maggots (larvae) tunneling through the flesh. Larvae are rarely seen.
How to protect your trees from apple maggot
Keep your garden clean
- Frequently pick up and remove any apples that fall during the growing season and after harvest.
- Place these apples in the trash or send them to a municipal composting site.
- Do not compost them in your yard.
Removing overripe and rotten apples from around your trees can help reduce apple maggot infestations, however, it will not prevent apple maggot flies that come in from other areas.
This method was developed in western Minnesota and should be used after you thin the fruit in early to mid June.
- Enclose each apple in a plastic sandwich bag, either a zipper closure bag or a plain bag closed with staples.
- Snip the bottom corners off each bag with a pair of scissors to leave a small opening for water to run out.
- At harvest, remove the bag.
Bagging fruit takes extra time , however, the apples are protected from apple maggots for the rest of the season.
Bagging is easy to do if you have a small to medium-sized tree that can be managed from the ground or a short ladder.
If you have a tall tree, you may choose to bag only the fruits that are easy to reach, and let the apple maggots have the higher fruits.
Using sticky traps
The trap-out method uses sticky traps to capture apple maggot females that attempt to lay eggs on the fruit.
Apple maggot traps are red spheres coated with tanglefoot, a sticky substance that permanently holds insects.
Options for apple traps are:
- Wooden or plastic spheres painted red.
- Red plastic spheres designed and sold specifically for this purpose.
- Store-bought large, red, fresh apples coated with tanglefoot. Compost them at the end of the season.
Whichever type of trap you choose, the spheres or apples should be at least 3 inches in diameter and bright red.
- Hang up wooden spheres with an eye screw and a wire hook. Hang up fresh apples by skewering the apple with a coat hanger and bending the excess wire into a hook.
- Hang scent lures (that smell like the apple fruit) with your traps to make them more attractive to flies.
A variant of the red sphere is the Ladd trap, a red sphere/yellow rectangle combination. This trap may be more effective in catching apple maggot flies. It may be better to use the Ladd trap, even if they are more difficult to clean.
You may also choose to purchase scent lures to hang with your traps to increase their attractiveness to flies. The lures contain volatile chemicals that apple maggot flies perceive as the scent of apple fruit.
Hang one trap per 100 fruit (after thinning) in each tree.
- One or two spheres for small trees and five or more traps for larger trees.
- Place at least one trap on the side of the tree that faces any wooded or brushy area.
- A second trap should hang on the south side of the tree.
If there are apple or hawthorn trees in wooded or landscaped areas nearby, you may want to hang traps in these trees as well, to further reduce apple maggot pressure.
- Hang traps in the trees by the end of June, to catch the apple maggot flies as they first attempt to lay eggs.
- Remove any leaves or fruit touching the traps.
- Check all the traps weekly. Clean off the tanglefoot-coated insects and apply more tanglefoot, as needed .
Using kaolin clay
Kaolin clay can discourage apple maggot flies and other insects from laying eggs in apple plantings. This method is best used with traps and before any pesticide application.
- Apply in a visible layer to all surfaces of the tree, leaves and fruit. This acts as a visual and physical repellent to insects.
- Apple maggot females are attracted to the red color of ripening apples, so a grayish-white apple is not attractive to them.
- The layer of clay on fruits repels many insects and they may leave immediately.
The clay washes off easily even in moderate rain and may not provide enough coverage. As fruits expand, coverage must be renewed frequently. A very well maintained coating of kaolin clay can protect 90% of fruit from apple maggots, although effectiveness may be only as high as 30% of the apples.
Check for the presence of apple maggots using sticky red spheres. This will help you decide if you should apply a pesticide.
- Check the trap frequently.
- If you do not use a scent lure, spray for apple maggots as soon as you catch a single adult.
- If you hang a trap with a lure, wait until you have caught a total of five flies.
Effective pesticides available for apple maggot control are: esfenvalerate, carbaryl and spinosad.
Traps need to be cleaned after each spray. Reapply tanglefoot if needed and begin checking the traps every day or two as before.
- Spray again and repeat the whole process, as needed.
- You might have to spray for apple maggot three or four times per season.
Fortunately, the number of apple maggot adults reduces as the season progresses and you should be able to stop spraying sometime in August.
CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.
Be sure that the fruit/vegetable you wish to treat is listed on the label of the pesticide you intend to use. Also be sure to observe the number of days between pesticide application and when you can harvest your crop.
Reviewed in 2018